1. Field of the Invention
The invention pertains to the detection of sub-micron particles, particularly particles below about 0.3 microns in average diameter, present on the surface of a bare (planar) substrate as contaminates. Particular attention is paid to the detection of particles on substrates for integrated circuit manufacture.
2. Background of the Prior Art
Recent developments in integrated circuit technology have seen a rapid shift to increased density and decreased spacing of circuit elements in integrated circuits. All indications are that this trend will increase, and perhaps accelerate, in the next few years. Particulate contaminates present on the surface of a substrate on which a IC is built are potentially capable of causing fatal defects to the IC. Accordingly, there is a need to detect, and thereby eliminate sub-micron sized particles from an IC wafer surface. Particles below 0.1 micron in size, about 0.05 microns, present on the wafer surface can greatly reduce yield, at the current level of semi-conductor technology. As density values increase, the diameter of the particle likely to cause a fatal defect will shrink.
Currently available technology to detect the presence of small particles rests principally with laser surface scanners. Although a wide variety are available, they are generally incapable of resolving particles smaller than about 0.2-0.3 microns. While scanning electron microscopes can resolve particles much smaller than this, they scan extremely smaller areas, at any given time. The scanning process for a relatively small wafer, i.e., 3-4 inches, extends over several hours. This is simply not consistent with commercial demands. Accordingly, it remains a pressing object of the industry to provide a swift, reliable method for detecting particles smaller than about 0.3 microns average diameter on the surface of a wafer or other IC substrate, which technique requires a relatively short time.